It is known that any conventional endless conveyor belt constantly undergoes more or less considerable deformation in operation, and requires adequate tensioning to enable it to be driven by a drive drum. However, this deformation involves a loss of energy and the risk of more or less rapid deterioration of the belt, and for this reason should be limited as far as possible. It is for this reason that the belt is generally guided and supported along its path by series of rollers, the spacing between which is selected in dependence upon the tension of the belt, its rigidity, the load to be supported, etc. so as to reduce deformation to acceptable limits. For example, the longitudinal spacing of the rollers can be of the order of 1 meter in the case of a belt used for conveying bulk goods, whereas it is generally only 10 to 20 cm in the case of a belt of the kind used for carrying passengers, not only to reduce deformation but also to provide an adequate level of comfort.
In most conventional conveyor belts, the rollers involve fairly considerable capital investment and, in addition, have to be regularly serviced at not inconsiderable expense. Accordingly, there is an obvious advantage in reducing the number of rollers associated with a conveyor belt as far as possible while, at the same time, avoiding any increase in the deformation of the conveyor belt. However, it would only be possible by using a belt of high longitudinal rigidity to reduce the number of rollers by increasing the spacing between them while, at the same time, keeping deformation of the belt within acceptable limits. However, the conveyor belt has to have adequate longitudinal flexibility to enable it to follow the changes in level imposed by its travel and, in particular, to travel satisfactorily around return drums of fairly small diameter. Accordingly, there are two incompatible requirements to be satisfied, namely high longitudinal rigidity and flexibility. It has not been possible in conventional conveyors to solve this problem, rather has it always been necessary to make a compromise between these two requirements and, hence, to use a more or less large number of rollers to limit longitudinal flexure of the conveyor belt along the straight sections of its path intended for conveying loads.
For example, conveyors comprising a main endless belt intended for conveying loads and driven by one or more auxiliary belts, have been in use for some time. The auxiliary belts enable the cross-section of the main belt to be limited, especially in the case of a very long conveyor, thereby limiting the tensile stresses to which the belt is subjected.
Unfortunately, the use of auxiliary drive belts of this kind hardly enables the longitudinal flexure of the main belt to be limited to any appreciable extent, with the result that the conveyor still has to be provided with rollers in the same way as other conventional belt conveyors.
In addition, belts arranged in such a way as to obtain high transverse rigidity are also known. It is possible in this way, for example, to improve the level of comfort in cases where the belt is used for carrying people. However, it is necessary in this case as well to provide the conveyor with a large number of rollers in order to limit flexure of the belt in the longitudinal direction.
Accordingly, it is not possible in conventional belt conveyors to reduce the number of rollers used without undesirably increasing deformation of the belt along the straight sections of its path intended for carrying loads.